Multi-layer paper formation wherein outer layers are substantially free of bod substances

ABSTRACT

In a process for the manufacture of paper or a similar fibre sheet product the initial fibre-stock suspension, which contains BOD substances, is divided into two fibre suspension flows. One of these fibre suspension flows is conveyed to a first sheet forming stage wherein a first fibre layer is formed and dewatered. The second fibre suspension flow is first subjected to a washing process in which the original suspension water containing BOD substances is exchanged for new suspension water which is substantially free from BOD substances, and is after this washing process conveyed to one or more additional sheet forming stages wherein one or more additional fibre layers are formed and dewatered. These additional fibre layers are joined with the first fibre layer from the first sheet forming stage into a multi-layer fibre web, which is passed through a press section for further dewatering. The backwater from the first sheet forming stage and the exchanged suspension water containing BOD containing substances from the washing process is recirculated to the initial fibre-stock suspension. The backwater from the additional sheet forming stages and from the press section is preferably recirculated to the washing process and used therein for the substitution of the original suspension water containing BOD containing substances in the second fibre suspension flow.

United States Patent 11 1 g pg 1111 3,821,073 Eriksson 1 1 145 June 28,1974

[ MULTI-LAYER PAPER FORMATION [57] ABSTRACT WHEREIN OUTER LAYERS ARE SUBSTANTIALLY FREE OF BOD In a process for the manufacture of paper or a similar SUBSTANCES fibre sheet product the initial fibre-stock suspension, [75] Inventor; Erik Sture Erikss n, Karlstad, which contains BOD substances, is divided into two Sweden fibre suspension flows. One of these fibre suspension Y flows is conveyed to a first sheet forming stage [73] Asslgneeafimg gfifi g m f wherein a first fibre layer is formed and dewatered.

The second fibre suspension flow is first subjected to a [22] Fil d; On, 2, 1972 washing process giowhiclg the original suspensiton I 1 water containing D su stances is exchanged or [21] Appl' 294020 new suspension water which is substantially free from BOD substances, and is after this washing process con- [30] Foreign Application Priority Data veyed to one or more additional sheet forming stages Oct. 15, 1971 Sweden 13117/71 wherein we of more additional fibre layers are formed and dewatered. These additional fibre layers 52 us. c1 162/126, 162/127, 162/190, 1 are 19 Withthe first fibre layerfrom the firstsheet 162/203 162/264 162/300, 162/303 forming stage into a multi layer fibre web, which is 511 1m. (:1 ..n21r1/s0,1)21r 11/04 1 Passed through a Press teeth) for further dewaterihg- 58 Field Of Search 162/190, 264, 123, 127, 1 The backwater from the first Sheet formmg Stage and 162]]32 189 13 100, 126 203, 300 I the'exchanged suspension water containing BOD containing substances from the washing process is recircu- 56] References Cited late? to th; filial?! fibrel-stfiick xi uspe nsion. The baciiclf water rom t e a mom 5 eet orming stages an rom UNITED STATES PATENTS 1 the press section is preferably recirculated to the RCIEZei X n proce and used therein for the ubstitution 5 322 :32; g i' of the original suspension water containing BOD con- 3:471:36? 10]]969 162/123 X taining substances in the second fibre suspension flow.

3,543,834 12/1970 Stuebe l62/300 Primary Examiner-S. Leon Bashore 1 Assistant Examiner-Richard H. Tushim 13 Claims, 2 Drawing ijgures Attorney, Agent, or Firm-Brumbaugh, Graves, Dono- .1 hue & Raymond Grinding 7 Screening 1 Washing 325/1134, 3Z5m /h 79 T 1:1 M 4 17 0,9111% 25d 3nd 1a Fam/hg irm/hg H Stage Stage zsm% m 3575111 1: B3575/03/11 ,2.3m /h 1 MULTI-LAYER PAPER FORMATION WHEREIN OUTER LAYERS ARE SUBSTANTIALLY FREE OF BOD SUBSTANCES BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for the manufacture of paper or similar fibre sheet products without any discharge of water polluting, biochemically oxidizing substances from the production process. The invention is also related to a apparatus in which the process according to the invention is used.

2. Description of the Prior Art The fibre-stock suspensions used for the manufacture of paper and similar fibre sheet products by wet form ing contain generally substantial amounts of biochemically oxidizing substances, so called BOD (biochemical oxygen demand) substances, which originate from the preparation of the fibre-stock and which are contained in the suspension water which is removed from the fibre suspension at the dewatering thereof in the paper manufacturing process. These BOD substances consist partly of suspended organicsubstances, as fines, bark, resin and fat, and partly of dissolved organic substances, as lignin, hydrocarbons, organic acids and alcohols. Consequently, the white water or backwater from the sheet forming section and the press section of a paper machine contains generally a substantial amount of such BOD substances, wherefore it has be come more and more obvious that such backwater cannot be permitted to be discharged into rivers and lakes, where it will give cause to an unacceptable water pollution. Basically there are two alternative methods of tackling this problem. One method is to take such steps at the production of the fibre-stock, i.e., at the production of the paper pulp, that the resulting pulp does not contain any BOD substances which can pollute the backwater in the subsequent paper manufacturing process. This must of course be done in such a manner that the pulp production itself does not give cause to any discharge of water containing BOD substances. Such a method involves however considerable problems. The solid, suspended BOD substances may certainly in principle be removed by filtration or settling but can hardly be recirculated to the pulp production process but must be destroyed or made harmless in some other way. The dissolved BOD substances on the other hand cause still more difficult problems, as they cannot be removed by mechanical means. The other, alternative method is to take care of the BOD substances in the-backwater from the sheet forming and press sections of the paper ma chine used in the paper manufacturing process in such a way that these substances are not released into rivers or lakes. As mentioned above, the solid suspended BOD substances may be separated from the backwater by filtration or settling and either be destroyed or recirculated to the process, in which latter case, however, the recirculated BOD substances will cause a certain discolouration or yellowing of the manufactured paper. The dissolved BOD substances in the backwater, on the contrary. can only be taken care of by complete closing of the backwater system so that all backwater is recirculated to the process.

SUMMARY OF THE INVENTION The primary object of the present invention is therefore to provide an improved process for the manufacture of paper and similar fibre sheet products, in which it is possible to use as starting material a fibre-stock suspension containing BOD substances without any backwater containing BOD substances being discharged and without any discolouration or yellowing of the surface of the manufactured product due to the presence of BOD substances.

Another object of the invention is to provide a process for the manufacture of paper and similar fibre sheet products, which has a very low total water consumption and in which almost the entire amount of water necessary for the process is kept circulating in closed loops within the process.

An object of the invention is also to provide a plant for the manufacture of paper and similar fibre sheet products by means of a process according to the invention.

The process according to the invention comprises the steps of dividing an initial fibre-stock suspension, which contains BOD substances, into a first and a second fibre suspension flow;

conveying said first fibre suspension flow to a first sheet forming stage, in which a first fibre layer is fonned and dewatered;

subjecting said second fibre suspension flow to a washing process by exchanging the original, BOD substances containing, suspension water for new suspension water which is substantially free from BOD sub tances;

conveying said second fibre suspension flow after said washing process to at least one additional sheet forming stage, in which at least one additional fibre layer is formed and dewatered;

joining said first fibre layer and said additional fibre layer to form an at least two-layer fibre web; and

recirculating the backwater from said first sheet forming stage and the suspension water, containing BOD substances, which are removed from said second fibre suspension flow in said washing process to said initial fibre-stock suspension.

A particularly preferred embodiment of the process according to the invention comprises the additional step of recirculating the backwater from said additional sheet forming stage to said washing process to be used therein as new suspension water to be substituted for the original, BOD substances containing, suspension water in said second fibre suspension flow.

Using the process according to the invention, paper or a similar fibre sheet product is manufactured in two or preferably three or still more layers, and the BOD substances originally contained in the initial fibre-stock suspension are substantially concentrated in one of these layers and particularlyin the central layer in a product containing three or more layers. ln this way any discharge of water-carried BOD substances from the manufacturing process is eliminated and at the same time the two surface layers of the product or at least one surface layer of the product, if the product consists of only two layers, will remain free from any BOD substances that may cause a dliscolouration or yellowing of the surface. As in the process according to the invention all backwater is recirculated in the pro cess, so that the backwater system is completely closed, the total water consumption for the process will be very small. This gives the additional very important advantage that a manufacturing plant operated in accordance with the process of the invention does not have to be located close to a large source of water, as for instance a river or lake.

BRIEF DESCRIPTION OF THE DRAWINGS The invention and additional advantageous features thereof will be described more in detail in the following with reference to the accompanying drawings, in which FIG. 1 shows by way of example a flow diagram for a production of newsprint, in which a process according to the invention is used; and

FIG. 2 shows schematically a paper machine which may be used for the production illustrated in FIG. ll.

DESCRIPTION OF EMBODIMENTS In the flow diagram shown in FIG. l for a production of three-layer newsprint by means of a process according to the invention the pulp or fibre-stock suspension flows are shown by double solid lines whereas the water fiows are shown by single solid lines. The numerical data given adjacent the various flows indicate by way of example the volumes of water in the various flows in cubic metre per ton of produced paper.

In a grinding process I, to which wood and water enclosed in and adhering to the wood is supplied at 2, wood is ground in conventional manner to wood-pulp, which is transferred to a screening process 3, in which more water is added at 4 and the pulp is processed in conventional manner to the fibre-stock suspension to be used for the paper production. This initial fibrestock suspension from the screening stage 3 is divided in two suspension flows 5 and 6. This division of the initial fibre-stock suspension in two separate suspension flows may, when desired, also involve a quality discrimination with respect to for instance the fibre length of the stock in the two suspension flows 5 and 6. Both these fibre suspension flows 5 and 6 will contain BOD substances.

The suspension flow 5 is conveyed directly to a first sheet forming stage 7 for the forming and dewatering of a first fibre layer 8. The entire amount of backwater from this first sheet forming stage 7 is collected and recirculated to the process; in the illustrated example of the invention to the screening process 3.

The second fibre suspension flow 6 is conveyed to a washing process 9, in which the fibre suspension 6, which contains BOD substances, is washed or treated with water supplied at M), which is substantially free from BOD substances, in such a manner that the original, BOD substances containing, suspension water is exchanged for new suspension water which is substantially free from BOD substances. Consequently, the washing stage 9 provides a fibre suspension flow ll which is substantially free from BOD substances. The BOD substances originally contained in the fibre suspension flow 6 are discharged from the washing process 9 together with the suspension water which has been exchanged in the washing process, as a water flow 12 which is recirculated to the initial fibre-stock suspension; in the illustrated example to the screening process 3. Various types of washing devices for such an exchange of the suspension water in a fibre-stock suspension are well known in the art, wherefore they do not have to be described in detail. Examples of appropriate washing devices are described and shown in US. Pat.

No. 3,088,306, No. 3,419,466, No. 3,616,660 and Canadian Pat. No. 645,650 and No. 839,522.

The fibre suspension flow 11 from the washing stage 9, which is free from BOD substances, is in the illustrated example of the invention divided in two suspension flows which are conveyed to a second sheet forming stage 13 and a third sheet forming stage M respectively. In the second sheet forming stage 13 a second fibre layer is formed and dewatered. This second fibre layer from the second sheet forming stage 13 is joined with the first fibre layer 18 from the first sheet forming stage 7 to a two-layer fibre web 15, which is subsequently joined with a third fibre layer, which is formed and dewatered in the third sheet forming stage 14, so that finally a three-layer fibre web 16 is obtained. The different fibre layers are joined to form the ultimate multi-layer fibre web in such a manner that the fibre layer 8 formed in the first sheet forming stage 7 will be disposed between the two fibre layers formed in the additional sheet forming stages 13 and 14. In the second sheet forming stage l3 the second fibre layer is preferably formed and dewatered in contiguity with the one side of the fibre layer 8 produced in the first sheet forming stage 7, whereas in the third sheet forming stage M the third fibre layer is formed and dewatered in contiguity with the opposite side of the first fibre layer 118 in the two-layer fibre web l5 transferred from the second sheet forming stage 13. Alternatively, however, the different fibre layers may be formed and dewatered separately and subsequently joined to form the final multi-layer web. Whether the one or the other method is used is of secondary importance for the process according to the invention and is primarily determined by the type of paper-making machine being used.

The resulting multi-layer fibre web 16 is subsequently passed through a press section l7 for additional dewatering and thereafter conveyed to a dryer section (not shown in the drawing), in which the remaining water in the paper web 18 leaving the press section 117 is removed. In conventional manner a certain amount of clean water is supplied to the press section 17 and 19 for the cleaning of the press felts.

It is appreciated that the backwater from the sheet forming stages 13 and 14- and also from the press section 17 will be substantially free from any BOD substances, wherefore this backwater can be discharged into a river or lake without giving cause to any water pollution. However, the backwater from the sheet forming stages 13 and 14 and from the press section 17 is preferably collected and recirculated at 10 to the washing process 9, in which this backwater is used as the washing water, free from BOD substances, required for the washing of the fibre suspension flow 6. In this way a completely closed backwater system and thus a very low water consumption is obtained. In the illustrated example of the invention the water consumption is limited to the amount of water conveyed to the process together with the wood supplied to the grinding stage 1 and the amount of clean water supplied at 19 to the press section 17 for the cleaning of the press felts. A corresponding amount of water leaves the process together with the paper web 18 leaving the press section 17 and is consequently removed as steam at the subsequent drying of the paper web. The major portion of the very large water volumes necessary for the process are kept circulating in closed loops within the process. Due to the very low water consumption of the process, a paper manufacturing plant operating in accordance with the invention does not have to be located close to any large source of water, as for instance a river or lake.

It is also appreciated that the BOD substances contained in the pulp leaving the grinding stage 1 will be substantially exclusively concentrated into the fibre layer 8, which is formed in the first sheet forming stage 7 and which will constitute the central layer in the manufactured paper web, whereas on the other hand the fibre layers which are formed in the sheet forming stages 13 and 14 and which constitute the external surface layers in the manufactured paper web, will be substantially completely free from any BOD substances. Consequently, the manufactured paper will have surface layers which are not discoloured or yellowed by any BOD substances in spite of the fact that practically the entire amount of BOD substances contained in the original pulp will also be contained in the manufactured paper web, namely in its central layer 8, so that no water-carried BOD substances are discharged from the process. The inclusion of BOD substancesin the central layer 8 of the paper web does not normally caUse any deterioration of the quality of the final product. On the contrary it has often been found that the BOD substances give the central layer 8 and thus also the final paper web an increased strength. This increased strength is probably due to the fines in the BOD substances.

If a certain amount of chemical wood pulp shall be used in the newsprint production illustrated in FIG. 1 and described above, this chemical pulp is preferably added to the fibre suspension fiow 5 supplied to the first sheet forming stage 7, as indicated by a broken flow arrow 20, so that also the BOD substances in the chemical pulp will be incorporated in the central layer 8 of the final paper web. 1

In the embodiment of the invention illustrated by way of example in FIG. 1 the entire backwater volume from the first sheet forming stage 7 and from the washing process 9 is recirculated to the screening process 3. However. it is obvious that at least a part of this backwatervolume could also be added directly to the fibre suspension flows 5 and 6 or be recirculated to the grinding process 1 or to any other process stage used for the preparation of the initial fibre-stock suspension.

In the press section 17 the three-layer fibre web is dewatered from both sides, wherefore water contained in the two surface layers of the fibre web, which are substantiailly free from any BOD substances, is removed and replaced with water originating from the central layer 8 which contains the BOD substances. in order to prevent the BOD substances in the central layer 8 from reaching the surfaces of the paper web so as to discolour the web surfaces or even getting out into the backwater from the press section, it is preferable to ad just the degree of dewatering of the central layer 8 in the first sheet forming stage 7 to such a value that the water content of the fibre layer 8 leaving the first sheet forming stage 7 doesnot exceed the total water content of the three-layer fibre web 18 leaving the press section 17.

Although the invention has been described in the foregoing as applied to a production of three-layer.

newsprint, it is obvious that the process according to the invention can be used with the same advantages also for the manufacture of a paper web including only two fibre layers, in which case, however, only one surface of the paper web will be free from BOD substances, or including more fibre layers than three. It is also appreciated that the invention can also be used for the manufacture of other fibre sheet products than paper, as for instance cardboard or fibreboard.

When using a process according to the invention for the manufacture of paper various types of papermaking machines usable for themanufacture of multilayer paper may be used. However, a paper-making machine of the type schematically illustrated in F IG. 2 is especially preferred.

The paper-making machine illustrated by way of example in FIG. 2 is adapted for the manufacture of three-layer paper and comprises consequently, in ac- The first sheet forming section 7 includes a first forming roll 21 and two endless screens or wires 22 and 23, which extend together, one upon the other, over a portion of the cylindrical surface of the forming roll 21 with the wire 22 closest to the forming roll 21. The wire 22 extends also over a number of guide and tension rolls 24; The other wire 23 extends over a number of guide and tension rolls 25 and also over a first couch roll 26 as well as over a second forming roll 27 in the second sheet forming section 13. At the first forming roll 21 the two wires 22 and 23 form between them a nip which converges in the direction of movement of the wires and the fibre suspension from a first headbox 28 is injected into this nip. A tray 29 for collecting the backwater being removed from the fibre sheet formed between the wires 22 and 23 is located radially outwards of the portion of the circumference of the first forming roll 21, over which the two wires 22 and 23 extend. The first forming roll 21 in the first sheet forming section 7 has an open, that is water-penetrateable, cylindrical wall, on the inside of which a suction box 30 is arranged within the portion of the circumference of the forming roll, over which the wires 22 and 23 extend. Further, there is an additional tray 31 for collecting the backwater from the forming roll 21.

The fibre suspension or slurry injected from the headbox 28 into the converging nip between the two wires 22 and 23 in the first sheet forming section 7 is dewatered in that the water is forced through the two wires 22 and 23 as these run together along a portion of the cylindrical surface of the forming roll 21. The

water being forced through the inner wire 22 flows through the perforated cylindrical wall of the forming roll 21 and is held within the forming roll 21 against the action of the centrifugal force by the suction from the suction box 30. When the effect of the suction box 30 upon the water ceases, due to the rotation of the forming roll 21, the water is thrown out from the forming roll into the tray 31. The portion of the suspension water being forced out through the outer wire 23 is in which further water is removed from the fibre sheet and this is separated from the wire 22 and transferred by the other wire 23 to the second sheet forming stage 13.

The second sheet forming section 13 is in principle of the same design as the first sheet forming section 7 and comprises consequently a second forming roll 27, over which the wire 23 extends as the inner wire, and a wire 33, which forms-the outer wire on the forming roll 27 and extends over guide and tension rolls 34, a second couch roll 35 and a third forming roll 36 in the third sheet forming section 14. A second headbox 38 for this second sheet forming section 13 injects the fibre-stock suspension into the converging nip between the wires 33 and 23 at the second forming roll 27. From this injected fibre suspension a second fibre layer is formed and dewatered upon the fibre layer produced in the first sheet forming section 7. By contrast with the first forming roll 21 in the first sheet forming section 7 the second forming roll 27 in the second sheet forming section 13 has a closed, impermeable surface, wheretofore the newly formed fibre layer is dewatered only through the outer wire 33. The removed water is collected in a tray 39. At the second forming roll 2'7 it is in this way produced a fibre web in FIG. I) consisting of two layers, which web is conveyed between the two wires 23 and 33 to the second couch roll 35, which is provided with a suction zone 37, in which further water is removed from the second fibre layer produced in the secondsheet forming section 13, and where the two-layer fibre web is separated from the wire 23 so as to be transferred by the wire 33 to the third sheet forming section 14.

The third sheet forming section 14 is of an identical design with the second sheet forming section 13 and comprises consequently in addition to the third forming roll 36 and the wire 33, which functions as an inner wire at this forming roll, also an outer wire 40 extending over guide and tension rolls 41 and a third couch roll 42 provided with a suction zone 43, a third headbox 44 and a collecting tray 45 for the removed water.

The fibre suspension injected into the nip between the wires 40 and 33 from the headbox 44 forms a third fibre layer in contiguity with the fibre layer produced in the first sheet forming section 7 and this third fibre layer is dewatered through the outer wire 40. The removed water is collected in the tray 45. Consequently, at the third forming roll 36 there is produced a threelayer fibre web 16 in FIG. 1), in which the fibre layer produced in the first sheet forming section 7 forms the central layer and which is conveyed between the wires 33 and 40 to the third couch roll 42, within the suction zone 43 of which more water is removed from the last produced fibre layer and where the three-layer fibre web is separated from the wire 33 so as to be conveyed by the wire 40 to the press section 17. The three-layer fibre web is picked off from the wire 40 by an endless felt 47 running over a pick off roll 46 and is then additionally dewatered in the press section 17 to provide the fibre web [8 (compare FIG. I), which is conveyed to a dryer section not illustrated in the drawing.

When using the paper-making machine illustrated in FIG. 2 and described above for the production process illustrated in FIG. I the suspension flow 5 from the screening process 3 is supplied to the headbox 28 of the first sheet forming section 7, whereas the suspension flow 11 from the washing process 9 is supplied to the headboxes 38 and 44 in the second and third sheet forming sections 13 and 14 respectively. The backwater from the collecting trays 29 and 31 and from the first couch roll 26 in the first sheet forming section 7 is recirculated to the screening process 3 at 4, whereas the backwater from the collecting trays 39 and 45 and from the couch rolls 35 and 42 in the second and third sheet forming sections 13 and 14 respectively as well as the backwater from the press section 17 is recirculated to the washing process 9 at 10.

As the central layer of the paper web, which is formed in the first sheet forming section 7, is dewate red from both sides, a very effective dewatering and a completely symmetrically formed central layer is achieved. As in contrast hereto the forming folls 27 and 36 in the a two subsequent sheet forming sections 13 and 14 have closed, impermeable surfaces, the outer fibre layers formed on opposite sides of the central fibre layer are dewatered substantially only in one direction outwards from the central fibre layer. This gives the advantage that no dewatering worth mentioning will take place through an already formed and dewatered fibre layer, which could otherwise give cause to disturbances in this previously formed fibre layer. For the same reason the fibre suspension jet from the headboxes 38 and 44 in the sheet forming sections 13 and 14 respectively is directed slightly towards the outer wire 33 and 40 respectively so that the suspension jet does not destroy the fibre layer already present on the inner wire.

A paper machine designed as described above has also the advantage that all dewatering means along the wires consist of rotating rolls, which cause a very small wear upon the wires. It is appreciated that a papermaking machine of this type can readily be expanded with additional sheet forming sections for the manufacture of paper webs with more than three layers. It is also appreciated that a paper-making machine of a similar design may also be used for the manufacture of paper webs with only two layers.

What is claimed is:

l. A process for the manufacture of fibre sheet prodnets, in particular paper, using an initial fibre-stock suspension containing BOD substances comprising the steps of dividing said initial fibre-stock suspension into a first and a second fibre suspension flow;

conveying said first fibre suspension flow to a first sheet forming stage for the forming and dewatering ofa first fibre layer; subjecting said second fibre suspension flow to a washing process by exchanging the original, BOD substances containing, suspension water for new suspension water whic is substantially free from BOD substances;

conveying said second fibre suspension flow after said washing process to at least one additional sheet forming stage for the forming and dewatering of at least one additional fibre layer;

joining said first fibre layer and said additional fibre layer to form an at least two-layer fibre web; and

recirculating the water being removed from said first suspension flow in said first sheet forming stage and the original, BOD substances containing, suspension water being exchanged in said second fibre suspension flow in said washing process to said initial fibre-stock suspension.

2. A process as claimed in claim 1, comprising the additional step of recirculating the water being removed from said second fibre suspension flow in said additional sheet forming stage to said washing process and therein using it for substituting the original, BOD substances containing, suspension water in said second fibre suspension flow. H

3. A process as claimed in claim 1, comprising the additional steps of conveying said at least two-layer fibre web through a press section for additional dewatering of the fibre web; and recirculating the water being removed from said fibre web in said press section to said washing process and therein using it for substituting the original, BOD substances containing, suspension water in said second fibre suspension flow.

4, A process as claimed in claim 1, wherein the water being removed from said first fibre suspension flow in said first sheet forming stage and the original, BOD substances containing, suspension water being exchanged in said second fibre'suspension flow in said washing process is recirculated for use in the preparation of said initial fibre-stock suspension.

5. A process as claimed in claim 1, wherein said second fibre suspension flow is conveyed after said washing process to two or more additional sheet forming stages for the forming and dewatering of two or more additional fibre layers, which are joined with said first fibre layer formed and dewatered in said first sheet forming stage to a multi-layer fibre web in such a manner that said first layer will form a central layer in said multi-layer fibre web.

6. A process as claimed in claim 5, wherein said multi-layer fibre web is conveyed to a press section for additional dewatering and said first fibre layer is dewatered in said first sheet forming stage to a water content not exceeding the total water content of said multilayer fibre web when leaving said press section.

7. A process as claimed in claim 1, wherein said additional fibre layer is formed and dewatered in contiguity with said first fibre layer,

8. A process as claimed in claim 7, wherein said first fibre layer is dewatered from both sides at the same time in said first sheet forming stage, whereas said additional fibre layer formed in said additional sheet form ing stage is dewatered substantially only from the side facing away from said first fibre layer.

9. Apparatus for the manufacture of fibre sheet products, in particular paper, comprising a first sheet forming section for the forming and dewatering of a first fibre layer;

at least one additional sheet forming section for the forming and dewatering of at least one additional fibre layer;

means for joining said first fibre layer from said first sheet forming section and said additional fibre layer from said additional sheet forming section to a multi-layer fibre web;

a press section for the dewatering of said multilayer fibre web;

means for receiving a flow of an initial fibre-stock suspension and dividing this flow into at least a first and a second fibre suspension flow;

means for washing a fibre suspension by substitution of new water for the original water in the suspension;

means for conveying said first fibre suspension flow to said first sheet forming section;

means for conveying said second fibre suspension flow to said washing means and for conveying said second fibre suspension flow after being washed in i said washing means to said additional sheet forming section;

means for collecting backwater from said first sheet forming section and original suspension water being exchanged for new suspension water in said washing means and conveying it to said means for receiving and dividing the initial fibre-stock sus pension; and

means for collecting backwater from said additional sheet forming section and said press section and conveying this backwater to said washing means to be used as washing water therein.

10. Apparatus as claimed in claim 9, wherein said additional sheet forming section is adapted to form and dewater said additional fibre layer in contiguity with said first fibre layer being formed and dewatered in said first sheet forming section.

11. Apparatus as claimed in claim 9, comprising at least two such additional sheet forming sections for the forming and dewatering of one additional fibre layer each in contiguity with opposite sides of said first fibre layer being formed and dewatered in said first sheet forming section.

12. Apparatus as claimed in claim 9, wherein each sheet forming section comprises a rotatable forming roll, two endless wires extending one upon the other along a portion of the circumference of the cylindrical surface of said forming roll so as to confine a nip between them at said forming roll, which nip converges in the direction of movement of said wires, and means for injecting a fibre suspension in said nip; the outermost of said two wires at the forming roll in a given sheet forming section constituting also the innermost wire at the forming roll in the next sheet forming section.

13. Apparatus as claimed in claim 12, wherein said forming roll in said first sheet forming section has an open, water-permeable, cylindrical surface, whereas said forming roll in said additional sheet forming sec tion has a closed, impermeable, cylindrical surface. 

2. A process as claimed in claim 1, comprising the additional step of recirculating the water being removed from said second fibre suspension flow in said additional sheet forming stage to said washing process and therein using it for substituting the original, BOD substances containing, suspension water in said second fibre suspension flow.
 3. A process as claimed in claim 1, comprising the additional steps of conveying said at least two-layer fibre web through a press section for additional dewatering of the fibre web; and recirculating the water being removed from said fibre web in said press section to said washing process and therein using it for substituting the original, BOD substances containing, suspension water in said second fibre suspension flow.
 4. A process as claimed in claim 1, wherein the water being removed from said first fibre suspension flow in said first sheet forming stage and the original, BOD substances containing, suspension water being exchanged in said second fibre suspension flow in said washing process is recirculated for use in the preparation of said initial fibre-stock suspension.
 5. A process as claimed in claim 1, wherein said second fibre suspension flow is conveyed after said washing process to two or more additional sheet forming stages for the forming and dewatering of two or more additional fibre layers, which are joined with said first fibre layer formed and dewatered in said first sheet forming stage to a multi-layer fibre web in such a manner that said first layer will form a central layer in said multi-layer fibre web.
 6. A process as claimed in claim 5, wherein said multi-layer fibre web is conveyed to a press section for additional dewatering and said first fibre layer is dewatered in said first sheet forming stage to a water content not exceeding the total water content of said multi-layer fibre web when leaving said press section.
 7. A process as claimed in claim 1, wherein said additional fibre layer is formed and dewatered in contiguity with said first fibre layer.
 8. A process as claimed in claim 7, wherein said first fibre layer is dewatered from both sides at the same time in said first sheet forming stage, whereas said additional fibre layer formed in said additional sheet forming stage is dewatered substantially only from the side facing away from said first fibre layer.
 9. Apparatus for the manufacture of fibre sheet products, in particular paper, comprising a first sheet forming section for the forming and dewatering of a first fibre layer; at least one additional sheet forming section for the forming and dewatering of at least one additional fibre layer; means for joining sAid first fibre layer from said first sheet forming section and said additional fibre layer from said additional sheet forming section to a multi-layer fibre web; a press section for the dewatering of said multilayer fibre web; means for receiving a flow of an initial fibre-stock suspension and dividing this flow into at least a first and a second fibre suspension flow; means for washing a fibre suspension by substitution of new water for the original water in the suspension; means for conveying said first fibre suspension flow to said first sheet forming section; means for conveying said second fibre suspension flow to said washing means and for conveying said second fibre suspension flow after being washed in said washing means to said additional sheet forming section; means for collecting backwater from said first sheet forming section and original suspension water being exchanged for new suspension water in said washing means and conveying it to said means for receiving and dividing the initial fibre-stock suspension; and means for collecting backwater from said additional sheet forming section and said press section and conveying this backwater to said washing means to be used as washing water therein.
 10. Apparatus as claimed in claim 9, wherein said additional sheet forming section is adapted to form and dewater said additional fibre layer in contiguity with said first fibre layer being formed and dewatered in said first sheet forming section.
 11. Apparatus as claimed in claim 9, comprising at least two such additional sheet forming sections for the forming and dewatering of one additional fibre layer each in contiguity with opposite sides of said first fibre layer being formed and dewatered in said first sheet forming section.
 12. Apparatus as claimed in claim 9, wherein each sheet forming section comprises a rotatable forming roll, two endless wires extending one upon the other along a portion of the circumference of the cylindrical surface of said forming roll so as to confine a nip between them at said forming roll, which nip converges in the direction of movement of said wires, and means for injecting a fibre suspension in said nip; the outermost of said two wires at the forming roll in a given sheet forming section constituting also the innermost wire at the forming roll in the next sheet forming section.
 13. Apparatus as claimed in claim 12, wherein said forming roll in said first sheet forming section has an open, water-permeable, cylindrical surface, whereas said forming roll in said additional sheet forming section has a closed, impermeable, cylindrical surface. 